1. Field of the Invention
The present invention is directed to telephony systems. More particularly, the present invention is directed to systems and methods for providing telephony services to a plurality of subscriber lines over a packet network.
2. Background
High speed data networks, such as the Internet, have emerged as viable platforms for the delivery of telephony services. For example, cable operators are currently utilizing hybrid fiber-coaxial (HFC) networks to deliver packet telephony services to subscribers via residential cable modems. It is anticipated that cable modem systems will enable the deployment of telephony services in a manner that is less costly than existing circuit-switched alternatives, as well as permit the delivery of unique value-added features, such as integrated voice mail and e-mail messaging.
The North American telephone market includes both single family dwellings and multiple dwelling units. According to conventional industry usage, the abbreviation “MDU” is used to refer both to multiple dwelling units as well as to the telephony equipment used to service them. For the sake of clarity, throughout the rest of this document the term “MDU” will be used exclusively to refer to multiple dwelling units themselves, whereas the terms “MDU equipment,” “MDU system,” or “MDU telephony system” will be used to refer to the telephony equipment used in servicing them.
The demand for subscriber circuits in MDU applications comprises approximately 30% of all telephony installations. However, conventional deployments of voice telephony services using cable modem systems are supported entirely by equipment designed to meet the requirements of single family dwellings. For example, a conventional cable modem device adapted for delivering voice telephony services over an HFC network is designed to support only a limited number of subscriber lines, such as four subscriber lines, per cable modem. (As used herein, the term “subscriber line” generally refers to the line that connects a customer's telephone to one or more interfaces to a high speed data network.) Consequently, a device of this type is not suitable for deploying telephony services in an MDU with a large number of subscriber lines, such as in an apartment or other high-density structure. Although multiple devices of this type could be used to support a greater number of subscriber lines, such a deployment would be prohibitively expensive in light of the cost of the devices.
Furthermore, conventional cable modem devices for delivering voice telephony services over an HFC network utilize a single digital signal processor (DSP) for processing voice signals from one or more subscriber lines for transmission over the HFC network. Because a single DSP is used, each voice channel must be processed serially. Thus, if conventional devices were utilized to support a larger number of subscriber lines, the single DSP would act as a bottleneck, causing transmission delay that would cause a reduction in Quality of Service (QOS). A much more powerful DSP would have to be utilized in order to process a larger number of subscriber lines while maintaining a transmission rate that would not cause call quality to suffer. The use of a very powerful DSP, however, would cause a dramatic increase in the cost overall cost of the device.
What is desired, then, is a system and method for delivering packet telephony services via a cable modem system that is capable of supporting a greater number of subscriber lines per cable modem. Furthermore, the desired system and method should reduce delay in the processing of voice packets and provide for improved bandwidth utilization so that a satisfactory packet transmission rate, and therefore QOS, may be maintained. In addition, the desired system and method should be cost efficient, providing more attractive cost per line characteristics than conventional systems and methods for delivering packet telephony services via a cable modem system.